Once you've chosen a product, buy enough for everyone in your family who needs treatment. If the hair you're treating is longer than shoulder-length, you may need more than one bottle to complete the first application. Check the labels to figure out how much you need.

How to apply lice cream rinse or other OTC product

Follow the instructions on the label carefully. You may need to shake before using or follow other specific guidelines.

Check the ingredients to see whether the active ingredients include permethrin or pyrethrin and piperonyl butoxide.

Apply permethrin-based lice treatments to wet hair. Before applying, shampoo hair with a nonconditioning shampoo and towel dry, so that hair is still damp, but not dripping. Don't use any kind of regular cream rinse or conditioner beforehand. It can reduce the effectiveness of the treatment

Wrap an old towel around your child's shoulders, or have your child wear something that you don't mind getting wet or stained.

Have your child hold a towel over his face to keep the shampoo out of his eyes.

Wear rubber gloves when applying it if you have open cuts or scratches on your hands

Massage the product into the hair from the roots to the ends until the scalp and all hair is thoroughly saturated. Pay close attention to the hairline on the back of the neck and behind the ears. You may see lice falling out of the hair during the treatment.

Leave both types of medicine on for ten minutes. (Start the clock after you've finished applying the medicine to the entire head.)

Promptly rinse or wash hair, depending on the instructions for that particular product.

Cautions for use of over-the-counter lice-killing treatments:

Don't use any lice treatment more often than the instructions recommend.

Don't use different lice medications at the same time.

Don't wrap anything around your child's head (such as a towel or a plastic bag) while the product is in his hair.

Never use lice medicine on eyelashes, eyebrows, or anywhere near the eyes.

Don't use the medicine on skin with open cuts or scratches.

Don't use on children under 2 months old.

If you're pregnant, breastfeeding, or allergic to ragweed or chrysanthemums, ask your doctor before using these products.

Post-treatment comb-out

The American Academy of Pediatrics (AAP) says comb-outs are unnecessary, but many parents will do one anyway. In fact, the lice-killing product you use may include a plastic lice comb. Experienced nit-pickers consider those combs useless and recommend buying a good metal lice comb.

The lice treatment is supposed to kill 70 to 80 percent of the nits, but it won't remove them. They may come out with a proper comb-out, though.

If the lice seem just as active as before, consult your doctor. If you applied the treatment correctly and it's had no effect by the next day, the lice may be resistant to the product you used. A doctor can help determine whether you used it correctly and whether you should attempt a second application.

If the first treatment does seem to slow the infestation, continue to comb out the hair every day or two. The instructions for most products recommend applying the medication again about ten days after the first application, but the American Academy of Pediatricians says that nine days is the optimal time for the repeat application.

Reviewed by pediatric dermatologist Anthony J. Mancini, M.D., head of the division of dermatology at Children's Memorial Hospital in Chicago.

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